Geoarchaeology and Site Formation Processes Chapter 7 Geoarchaeology and Site Formation Processes

Outline The Law of Superposition Reading Gatecliff’s Dirt Gatecliff’s Stratigraphy Is Stratigraphy Really that Easy? Site Formation Processes: How Good Sites Go Bad Conclusion

Geoarchaeology Applies concepts and methods of the geosciences to archaeological research. Objectives: Place sites and artifacts in a context through the application of stratigraphic principles and dating techniques. Understand the natural processes of site formation.

The Law of Superposition In any pile of sedimentary rocks undisturbed by folding or overturning, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on. This principle seems simple, but it was a critical observation in the 17th century when formulated by Nicolaus Steno.

Fossil Footprints at Laetoli: Law of Superposition in Action For decades, specialists in human evolution argued that bipedalism must have arisen in response to tool use. Based on her knowledge of the region’s geology, Leakey guessed that the age of the footprints at Laetoli was more than a million years older than the oldest known tool use.

How Old Are the Footprints? Leakey worked with geologists Robert Drake and Garness Curtis, who processed a series of potassium-argon dates on samples from the major stratified layers recognized in the Laetoli area. The fossil hominid footprints are between 3.49 and 3.56 million years old. With the dating of the Laetolil footprints, Leakey showed that humans were bipedal long before they made stone tools.

What Happened to the Laetoli Footprints? When Leakey completed her work she backfilled the site with 2 feet of soil. After a few years, trees grew on the spot. In 1995, archaeologist Fiona Marshall unearthed the trees’ roots without disturbing the tracks. In 100 years, the footprints will be uncovered again and if possible safely removed to a museum.

Stratigraphic Profile: Laetoli

Reading Gatecliff’s Dirt Gatecliff Shelter has a 40-foot stratigraphic profile covering more than 7000 years. The Gatecliff sediments, like those of all archaeological sites, resulted from both natural processes and human behavior.

Physical Stratigraphy of Gatecliff Shelter Stratum Soil Nature of sediment Field designation Age (C-14 yr bp) 1 S-1 Rubble GU-14 0–1250 BP 2 Sand and silt Upper GU 13 1250 BP 3 S-2 Part of GU 12 1250–1350 BP 4 GU 13 and GU 12 Silt 1350 BP 5 S-3 1350–3200 BP 6 GU 11 3200 BP 7 GU 11 and GU 10R 3250–3200 BP

Physical Stratigraphy of Gatecliff Shelter Stratum Soil Nature of sediment Field designation Age (C-14 yr bp) 8 Sand and silt GU 10 3250 BP 9 Rubble GU 9R 3300–3250 BP 10 GU 8 A and B 3300 BP 11 GU 7R 3400–3300 BP 12 GU 7 3400 BP 13 6 Living Floor 4050–3400 BP

Physical Stratigraphy of Gatecliff Shelter Stratum Soil Nature of sediment Field designation Age (C-14 yr bp) 14 Sand and silt GU 5 Silt 4050 BP 15 Rubble Part of GU 5 4100–4050 BP 16 4100 BP 17 GU 4 4250–4100 BP 18 Silty Sand GU 3 4250 BP 19 Sand and rubble GU 2 5000–4250 BP 20 S-4 Silt and clay GU 1A 5100–5000 BP 21 GU 1 and GU 7–74 5100BP

Physical Stratigraphy of Gatecliff Shelter Stratum Soil Nature of sediment Field designation Age (C-14 yr bp) 22 Rubble GU 6R–74 5250–5100 BP 23 Gravel, sand, and silt GU 6–74 and GU 5–74 5250 BP 24 GU 4R–74 5350–5250 BP 25 Silt GU 4-74 5350 BP 26 GU 3R-74 5500–5350 BP 27-29 Silts GU 3A-74 5500 BP 30 Sand GU 3B-74

Physical Stratigraphy of Gatecliff Shelter Stratum Soil Nature of sediment Field designation Age (C-14 yr bp) 31 Rubble GU 2R-74 5700–5500 BP 32 Fine sand, silt GU 2-74 33 GU 12–76, GU 1–78, GU 1–74 34 Silt, very fine sand GU 2–78 35 GU 3R–78 36 Silty medium sand GU 3–78

Hypothetical Rockshelter, Filling with Colluvial and Eolian Sediments, and Rooffall

Development of a Hypothetical Archaeological Site

Development of a Hypothetical Archaeological Site

Context A systemic context is a living behavioral system wherein artifacts are part of the on-going system of manufacture, use, re-use, and discard. Once artifacts enter the ground, they are part of the archaeological context, where they can continue to be affected by human action, but where they also are affected by natural processes.

Formation Processes in the Systemic Context Four key processes in the systemic context influence the creation of archaeological sites: Cultural deposition Reclamation Disturbance Reuse

Cultural Deposition Dominant factor in forming the archaeological record. Discard - Everything eventually breaks or wears out and is discarded. Loss - Example: An arrow that misses its target or a pot left at a camp. Caching - Some items are intentionally left behind. Ritual - Example: grave goods.

Reclamation Processes Human behaviors that result in artifacts moving from the archaeological context back to the systemic context. Example: scavenging beams from an abandoned structure to use them in a new one.

Cultural Disturbance Processes Human behaviors that modify artifacts in their archaeological context. Example: dam building; farming; and construction of houses, pits, hearths, and so on.

Reuse Processes In this process, an object moves through a series of behavioral settings before it enters the archaeological record. This can entail the recycling of some objects: Potsherds are ground up and used as temper in manufacturing new vessels. Broken arrowheads are re-chipped into drills.

Formation Processes in the Archaeological Context Once an object enters an archaeological context, a host of natural as well as cultural formation processes takes place. These natural processes determine whether organic material will be preserved and where objects will be found.

Natural Formation Processes Floralturbation - Process in which trees and plants affect the distribution of artifacts. Faunalturbation - Process in which animals, from large game to earthworms, affect the distribution of material. Cryoturbation - Process in which freeze/thaw activity in a soil pushes larger artifacts to the surface of a site.

Natural Formation Processes Argilliturbation - Process in which wet/dry cycles in clay-rich soils push artifacts upward as the sediment swells and then moves them down as cracks form during dry cycles. Graviturbation - Process in which artifacts are moved downslope through gravity, sometimes assisted by precipitation runoff.

Effects of Natural Formation Processes on Distribution of Artifacts

Effects of Natural Formation Processes on Distribution of Artifacts

Effects of Natural Formation Processes on Distribution of Artifacts

Effects of Natural Formation Processes on Distribution of Artifacts

Effects of Natural Formation Processes on Distribution of Artifacts

Site Formation Process Summary Systemic context Archaeological Context Cultural Deposition Floralturbation (plants) Discard Faunalturbation (animals) Loss Cryoturbation (freezing) Caching Argilliturbation (wet-dry cycles) Ritual interment Graviturbation (hill slopes) Reclamation Disturbance Reuse

How Artifacts Become Oriented to the Direction of River Flow

Quick Quiz

1. The _____ ______ ________ states that in any pile of undisturbed sedimentary rocks, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on.

Answer: Law of Superposition The Law of Superposition states that in any pile of undisturbed sedimentary rocks, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on.

2. When Leakey dated the Laeotolil footprints as between 3. 49 and 3 2. When Leakey dated the Laeotolil footprints as between 3.49 and 3.56 million years old, she showed that humans made stone tools long before they were bipedal. True False

Answer: B. False 2. When Leakey dated the Laeotolil footprints as between 3.49 and 3.56 million years old, she showed that humans were bipedal long before they made stone tools.

3. Floralturbation is a systemic site formation process caused by cultural deposition. True False

Answer: B. False Floralturbation is a natural formation process in which trees and plants affect the distribution of artifacts.

4. Scavenging beams from an abandoned structure to use them in a new one is an example of a _____ ______, human behaviors that result in artifacts moving from the archaeological context back to the systemic context.

Answer: reclamation processes Scavenging beams from an abandoned structure to use them in a new one is an example of a reclamation process, human behaviors that result in artifacts moving from the archaeological context back to the systemic context.